CCND1 and cancer: It is also well known that p53, which is closely associated with cancer inhibition, plays vital roles in a variety of intracellular and extracellular regulatory mechanisms, exerting its functions predominantly through the transcriptional activation of target proteins, such as Cdk 4, the Cdk inhibitor p21, and cyclin D1, to induce cell-cycle arrest, and the pro-apoptotic protein Bax to induce apoptosis [35].